Failure Detection, Isolation And Recovery Research Articles

Improving reliability and safety of airborne wind energy systems

AbstractAirborne wind energy systems use tethered flying devices to harvest wind energy beyond the height range accessible to tower‐based wind turbines. Current commercial prototypes have reached power ratings of up to several hundred kilowatts, and companies are aiming at long‐term operation in relevant environments. As consequence, system reliability, operational robustness, and safety have become crucially important aspects of system development. In this study, we analyze the reliability and safety of a 100‐kW technology development platform with the objective of achieving continuous automatic operation. We first outline the different components of the kite power system and its operational modes. In the next step, we identify failure modes, their causes, and effects by means of failure mode and effects analysis (FMEA) and fault tree analysis (FTA). Potentially hazardous situations and mechanisms which can render the system nonoperational are identified, and mitigation measures are proposed. We find that the majority of these measures can be performed by a failure detection, isolation, and recovery (FDIR) system for which we present a hierarchical architecture adapted from space industry.

Testing Satellite on-board Software - A Model Based Approach

Today, testing on-board software consumes approx. 30% of the effort for a software project. Improvements in this area will help to save a significant amount of time and money. As discussed in the research community, model based approaches are a very promising solution to save costs while increasing software quality at the same time. Failure Detection, Isolation and Recovery (FDIR) is a significant part of today's flight software. Approx. 30% of the test effort is spent on this functionality. The basis for the FDIR is the failure mode effect analysis (FMEA). Therefore, the approach we present hereafter starts from a “traditional” text based FMEA document.

Accurate and autonomous navigation for the ATV

The Automated Transfer Vehicle (ATV) is a European spacecraft intended to service the International Space Station (ISS). It is designed to perform automated phasing, approach, rendezvous and docking to the ISS, then departure and deorbitation manoeuvres. Such an automated rendezvous mission towards a manned facility raises severe performance and safety constraints for the vehicle, which are declined towards the on-board Navigation in terms of availability, accuracy and failure tolerance: the ATV shall be operational after any first failure and safe conditions shall be reached after a second failure. The whole ATV navigation system has been designed to fulfil these very stringent requirements. Based on fully redundant hardware, the navigation algorithms present optimal estimators and multi-layers Failure, Detection, Isolation and Recovery (FDIR) capabilities to ensure the continuity of the state vector in case of failure. Several functions provide state vectors estimations and health reports, according to the flight phase: the attitude and drift estimation function provides the vehicle absolute attitude and angular rate during the whole flight; for the far rendezvous, position and velocity relative to the ISS are estimated by the relative GPS navigation and a dedicated relative navigation with Videometer applies in close rendezvous, in the final approach. All these autonomous navigation functions offer nevertheless a high level of monitoring and control to the ATV Control Centre operators. Thus the ATV innovative navigation chain provides the high level of performance, robustness and autonomy required by modern spacecrafts involved in human programs, today in Earth orbit but also for future space exploration missions.

SMART-1: Development and lessons learnt

SMART-1 is the first of the small missions for advanced research and technology as part of ESA's science programme “Cosmic vision”. It was successfully launched on September 27, 2003 and is presently traveling towards its destination, the Moon. The main objective of the mission, to demonstrate solar electric primary propulsion for future Cornerstones (such as Bepi-Colombo), has already been achieved. At the time of writing the electric propulsion system has been working already for more than 3400 h and has provided a Delta-V to the spacecraft of more than 2500 m/s. The other technology objectives are also being fulfilled by the verification of the proper functioning of such on-board experiments like the X-Ka band transponder, the X-ray spectrometer, the near IR spectrometer, the laser link, etc. The scientific objectives are related to lunar science and will be fulfilled once the spacecraft enters its operational lunar orbit, currently expected for January 2005. SMART-1 lunar science investigations will include studies of the chemical composition of the Moon, of geophysical processes, environment and high-resolution studies in preparation for future steps of lunar exploration. SMART-1 has been an innovative mission in many aspects and we are now drawing some preliminary conclusions about the lessons to be learnt. The paper describes the spacecraft and the technology elements with particular emphasis to the technology nature of the mission. The on-board avionics employs many novel designs for spacecraft, including a serial CAN bus for data communication, autonomous star trackers and extensive use of auto-code generation for implementing the attitude control system and the failure, detection, isolation and recovery (FDIR). Finally, the orbital operation phase currently ongoing, including the routine electric propulsion operations and the instrument commissioning, is providing a wealth of data and lesson-learnt useful for future autonomous planetary missions.